The present invention relates to a gas component sensing apparatus for sensing, for example, an oxygen concentration of exhaust gases emitted from a vehicle engine.
One of the prior art apparatus of this type uses a metal oxide such as titanium oxide, an electrical resistance of which changes in accordance with the change in gas component density in a gas under test such as exhaust gas.
In a basic structure thereof, a pair of rod electrodes made of noble metal (Pt) are connected to a gas component sensor element mode of titanium oxide, the pair of electrodes are inserted in a holder made of heat resistance, electrically insulative metal oxide and the electrodes are fixed to lead members which are fixed to the holder.
The prior art sensing apparatus of the type described above, however, has the following drawbacks:
(1) In a two-wire sensing apparatus having a pair of electrodes, two electrodes and two lead members must be inserted in a holder of limited size, and hence the distance between the electrodes and the distance between the lead members are necessarily very short. Accordingly, holes must be formed in the holder very carefully to prevent the shortcircuit among the components.
(2) Since the distance between the lead members is short, the lead members cannot be connected to a connector of a control circuit unless a small size connector is used. Such a small size connector requires a complex construction and increases cost.
(3) As the connector becomes small and complex, it is difficult to design a connector which improves resistance to vibration, water proofing and resistance to heat at the junction of the connector and the lead members.